<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>CSS id 选择器</title>
  <style>
    #para1 {
      text-align: center;
      color: red;
    }
  </style>
</head>
<body>

<p id="para1">Hello World!</p>
<p>本段不受样式的影响。</p>

</body>
</html>